Natural disasters drove 42 million people from their homes in the Asia-Pacific in 2010 and 2011, though it was unclear how many of those were caused by climate change, the bank said in a study released Tuesday.

It said that one-third of Southeast Asia’s population lives in at-risk areas, including Indonesia, Myanmar, the Philippines, Thailand and Vietnam.

Six of the 10 countries most vulnerable to climate change are in the Asia-Pacific. Bangladesh tops the list followed by India, Nepal, the Philippines, Afghanistan and Myanmar.

The study did not make any specific projections for migration induced by climate change, noting that the numbers are difficult to estimate as migration decisions often depend on a wide array of factors, including poverty.

“Given that climate change acts as an aggravating factor for environmental degradation, it is expected to boost the number of people migrating because of environmental changes, both sudden and slow onset. Though the amplitude of these movements remains difficult to forecast, climate change is likely to become a major driver of migration in the 21st century,” it said.

It cited the Intergovernmental Panel on Climate Change, a U.N. network of 2,000 scientists, as saying that the Asia-Pacific will bear the brunt of significant temperature increases, changing rainfall patterns, greater monsoon variability, sea-level rise, floods, and more intense tropical cyclones. Most scientists expect such changes to accompany a rise in the planet’s temperature caused in part by greenhouse gasses from burning fossil fuels for electricity and transport.

The region is particularly vulnerable because of its high population density and long coastlines.

Recent examples of such migration include Papua New Guinea, where residents of Carteret and neighboring atolls moved to the island of Bougainville because of rising sea levels.

In 2010, more than 10 million Pakistanis were displaced by monsoon rains and flooding along the Indus River basin, and last year, a typhoon ravaged the southern Philippines, displacing more than 300,000 people.